A hydrogen fuel cell is an electrochemical device that efficiently converts the chemical energy stored in hydrogen and oxygen directly into electrical power, heat, and water. Unlike a battery that stores a finite charge, a fuel cell operates as long as a continuous supply of fuel is provided, making it an energy converter rather than a storage unit. Constructing a basic fuel cell serves as an excellent educational project to demonstrate the principles of clean energy generation. The most common and accessible type for this purpose is the Proton Exchange Membrane (PEM) fuel cell, which uses a solid polymer electrolyte.
Understanding the Electrochemical Reaction
The operation of a PEM fuel cell relies on an electrochemical process that separates a hydrogen molecule into its constituent parts to generate an electric current. Hydrogen gas is fed to the anode side, where a catalyst facilitates the splitting of the molecule into positively charged hydrogen ions, or protons, and negatively charged electrons. This reaction is known as the oxidation of hydrogen.
The specialized Proton Exchange Membrane in the center of the cell allows only the protons to pass through to the cathode side. Because the membrane is an electrical insulator, it forces the liberated electrons to travel along an external circuit to reach the cathode. This external pathway generates the usable electric current that powers a device.
Once they arrive at the cathode, the protons, the electrons from the external circuit, and oxygen gas recombine in a second reaction. This recombination, facilitated by a cathode catalyst, forms the byproduct: pure water. The overall reaction is a continuous, non-combustion process that produces electrical energy, with a single cell generating between 0.6 and 0.7 volts under operating conditions.
Gathering the Necessary Materials
The foundational component of the PEM fuel cell is the Membrane Electrode Assembly (MEA), which is the heart of the electrochemical reaction. This assembly requires several distinct, layered materials, beginning with the Proton Exchange Membrane itself, which is a thin, polymer film, often a sulfonated tetrafluoroethylene copolymer like Nafion. This membrane must be capable of conducting protons while remaining impermeable to the reactant gases and electrons.
Flanking the membrane are the Gas Diffusion Layers (GDLs), which are typically sheets of porous carbon paper or carbon cloth. The GDLs perform a dual function, distributing the reactant gases evenly across the active area of the membrane and providing an electrically conductive path for the electrons. These layers are often pre-treated or coated with a catalytic ink to form Gas Diffusion Electrodes (GDEs).
The catalytic ink is a slurry composed of fine platinum nanoparticles supported on carbon powder, mixed with an ionomer solution to enhance proton conductivity. Platinum is the preferred catalyst because it efficiently lowers the activation energy required for the reactions at both the anode and the cathode. The MEA is then held between graphite flow plates, which have machined channels to guide the hydrogen and oxygen gases to the GDLs and serve as current collectors.
Constructing the Membrane Electrode Assembly
The physical construction begins with creating the Membrane Electrode Assembly, requiring careful preparation of the catalyst layers. For a GDE-based assembly, the platinum catalyst ink is uniformly applied onto one surface of the carbon paper GDLs, often through spraying or painting. One coated GDL serves as the anode and the other as the cathode, with the catalyst-coated side facing the proton exchange membrane.
The next step involves fusing these layers together into a single, integrated assembly. The catalyst-coated sides of the GDLs are placed directly against the opposite sides of the PEM, forming a layered sandwich. This assembly is then subjected to hot-pressing, a process that uses both heat and pressure to ensure maximum surface contact and strong adhesion between the layers.
Following the hot-pressing, the completed MEA is positioned between gaskets and the flow field plates. The gaskets are placed around the active area to prevent gas leakage and to seal the MEA within the cell structure. The graphite flow plates, which feature channels, are aligned to ensure the gas channels directly face the GDLs, completing the electrical circuit and the gas delivery system. The cell is then clamped together using end plates to maintain the uniform compression necessary for optimal electrical and thermal contact.
Initial Operation and Safety Measures
Operating a newly constructed fuel cell requires strict adherence to safety protocols, particularly concerning the handling of hydrogen gas. Hydrogen is highly flammable and can ignite at concentrations as low as four percent in air. All assembly and testing must take place in a well-ventilated area, preferably with ventilation near the ceiling, since hydrogen is much lighter than air and will rapidly accumulate overhead.
Before introducing any reactants, all gas lines and connections must be checked for leaks. The hydrogen and oxygen supplies are then connected to the inlet ports of the flow plates, and the gases are introduced at a controlled, low pressure to begin the electrochemical reaction. For initial testing, a voltmeter is connected across the end plates to measure the open-circuit voltage, which should register close to the expected 0.9 to 1.0 volt range before any load is applied.
Once the open-circuit voltage is confirmed, a variable electronic load can be introduced to draw current from the cell, allowing for the measurement of the actual power output and the calculation of efficiency. Temperature and pressure gauges should be monitored to ensure the cell remains within its safe operating parameters. This controlled process verifies the successful construction and functionality of the device.